Auto-referenced memory cell read techniques

ABSTRACT

Methods, systems, and devices related to auto-referenced memory cell read techniques are described. The auto-referenced read may encode user data to include a predetermined number of bits having a first logic state prior to storing the user data in memory cells. The auto-referenced read may store a total number of bits of the user data having a first logic state in a separate set of memory cells. Subsequently, reading the user data may be carried out by applying a read voltage to the memory cells storing the user data while monitoring a series of switching events by activating a subset of the memory cells having the first logic state. During the read operation, the auto-referenced read may compare the number of activated memory cells to either the predetermined number or the total number to determine whether all the bits having the first logic state has been detected. When the number of activated memory cells matches either the predetermined number or the total number, the auto-referenced read may determine that the memory cells that have been activated correspond to the first logic state.

CROSS REFERENCE

The present Application for Patent is a divisional of U.S. patentapplication Ser. No. 15/853,364 by Mirichigni et al., entitled“Auto-Referenced Memory Cell Read Techniques,” filed Dec. 22, 2017,assigned to the assignee hereof, and is expressly incorporated byreference in its entirety herein.

BACKGROUND

The following relates generally to operating a memory array and morespecifically to auto-referenced memory cell read techniques.

Memory devices are widely used to store information in variouselectronic devices such as computers, wireless communication devices,cameras, digital displays, and the like. Information is stored byprograming different states of a memory device. For example, binarydevices have two states, often denoted by a logic “1” or a logic “0.” Inother systems, more than two states may be stored. To access the storedinformation, a component of the electronic device may read, or sense,the stored state in the memory device. To store information, a componentof the electronic device may write, or program, the state in the memorydevice.

Various types of memory devices exist, including magnetic hard disks,random access memory (RAM), read only memory (ROM), dynamic RAM (DRAM),synchronous dynamic RAM (SDRAM), ferroelectric RAM (FeRAM), magnetic RAM(MRAM), resistive RAM (RRAM), flash memory, phase change memory (PCM),and others. Memory devices may be volatile or non-volatile. Non-volatilememory cells may maintain their stored logic state for extended periodsof time even in the absence of an external power source. Volatile memorycells may lose their stored state over time unless they are periodicallyrefreshed by an external power source.

Improving memory devices, generally, may include increasing memory celldensity, increasing read/write speeds, increasing reliability,increasing data retention, reducing power consumption, or reducingmanufacturing costs, among other metrics. A more robust read techniquemay be desired to increase memory cell performance and reliability whenmemory cells exhibit variable electrical characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a memory device diagram having athree-dimensional (3D) array of memory cells that supportsauto-referenced memory cell read techniques in accordance withembodiments of the present disclosure.

FIG. 2 illustrates an example of a 3D memory array that supportsauto-referenced memory cell read techniques in accordance withembodiments of the present disclosure.

FIGS. 3A and 3B illustrate examples of user data patterns that supportauto-referenced memory cell read techniques in accordance withembodiments of the present disclosure.

FIGS. 4A and 4B illustrate techniques that support auto-referencedmemory cell read techniques in accordance with embodiments of thepresent disclosure.

FIGS. 5 and 6 show block diagrams of a device that supportsauto-referenced memory cell read techniques in accordance withembodiments of the present disclosure.

FIG. 7 illustrates a block diagram of a system including a memory arraythat supports auto-referenced memory cell read techniques in accordancewith embodiments of the present disclosure.

FIGS. 8 through 11 illustrate methods for auto-referenced memory cellread techniques in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

In some cases, memory cells exhibit non-uniform, variable electricalcharacteristics that may originate from various factors includingstatistical process variations, cycling events (e.g., read or writeoperations on the memory cells), or a drift (e.g., a change inresistance of a chalcogenide alloy), among others. Auto-referencedmemory cell read techniques of the present disclosure may provide areliable and robust read technique in which reading a set of user data(e.g., a codeword, a page) is carried out by tracking a number of memorycells activated in response to a read voltage applied to the memorycells. In some instances, the auto-referenced read may use apredetermined number to decide whether the memory cells associated witha first logic state have been accounted for while reading the user data.Further, the auto-referenced read may determine a total number of memorycells associated with the first logic state while reading the user data.

In some aspects, the auto-referenced read techniques reduces oreliminates a separate set of read-reference memory cells that may bepresent in a memory device. The read-reference memory cells may notpossess common electrical characteristics with a majority of memorycells in which user data are stored due to various reasons, such asdifferent process conditions (e.g., a non-uniform loading pattern of aplasma density) during fabrication process steps, a different cyclingevents, among others. Hence, the separate set of read-reference memorycells may not provide a reliable referencing scheme during a readoperation.

The auto-referenced read techniques may include an encoding scheme toapply to user data to establish a predetermined number of bits inencoded user data to have a given logic state (e.g., a logic state of 1)prior to storing the encoded user data in memory cells. The encodingscheme may include adding a number of extra bits (which may also bereferred to as parity bits) to the user data during the encodingprocess. In some embodiments, the auto-referenced read may use adifferent encoding scheme that stores a counting informationcorresponding to a total number of bits in the user data having a givenlogic state (e.g., a logic state of 1) in a number of memory cells whenstoring the user data. In some cases, the counting information may bestored as a binary number that represent the total number of bits in theuser data having the given logic state. In other cases, the countinginformation may be encoded to have a weight pattern of a given weight(e.g., 20%, 30%, 50% (i.e., one-half of the memory cells storing thecounting information have the given logic state), 75%).

In some aspects, a memory device may include an array of PCM cellsarranged in a 3D architecture, such as 3D XPoint™ memory to store userdata. PCM cells in 3D) XPoint™ architecture (which may also be referredto as 3DXP memory cells) may represent a first logic state (e.g., alogic state of 1) associated with a first set of threshold voltages or asecond logic state (e.g., a logic state of 0) associated with a secondset of threshold voltages. In some embodiments, a logic state of 1(e.g., a SET state of a PCM cell, which may also be referred to as a SETcell or bit) corresponds to a set of threshold voltages lower than a setof threshold voltages associated with a logic state of 0 (e.g., a RESETstate of a PCM cell, which may also be referred to as a RESET cell orbit).

The auto-referenced read techniques may include application of a voltage(e.g., a read voltage) to a memory array that is configured to activatea group of memory cells containing encoded user data. The voltage mayincrease as a function of time with a constant rate of change. In somecases, the read voltage has a monotonically increasing staircase shapesuch that a first voltage is applied for a first period of time followedby a second different voltage for a second period of time. The appliedread voltage may initiate a series of switching events by activating thegroup of memory cells storing the encoded user data. The switching eventmay be attributed to a memory cell turning on (e.g., conducting anappreciable amount of current) when the applied voltage across thememory cell exceeds its threshold voltage. The auto-referenced readtechniques may track a number of memory cells turning on (e.g.,activating) in response to the read voltage.

When the user data have been encoded with a predetermined number ofmemory cells to have a first logic state (e.g., a logic state of 1), theauto-referenced read techniques may compare the number of activatedmemory cells with the predetermined number stored in a memory device.When the number of activated memory cells is less than the predeterminednumber, the auto-referenced read techniques may continue to apply (e.g.,increase) the read voltage to the memory array while tracking additionalmemory cells that are activated (e.g., until the number of activatedmemory cells matches the predetermined number). When the number ofactivated memory cells matches the predetermined number, theauto-referenced read may stop applying the read voltage to the memoryarray and make a determination that all the activated memory cells ofthe encoded user data has the first logic state. Further, theauto-referenced read may determine that remaining memory cells of theencoded user data (e.g., the inactive memory cells when the number ofactivated memory cells matches the predetermined number) have a secondlogic state (e.g., a logic state of 0).

When the user data have been encoded with an additional set of memorycells that stores counting information corresponding to a total numberof bits in the user data having a first logic state (e.g., a logic stateof 1), the auto-referenced read techniques may read the countinginformation from the additional set of memory cells to identify thetotal number. The total number may be stored in a memory device toprovide a criterion as to whether a read voltage may continue or stopwhile tracking a number of activated memory cells of the user data inresponse to the read voltage. When the number of activated memory cellsis less than the total number, the auto-referenced read techniques maycontinue to apply (e.g., increase) the read voltage to the memory arraywhile tracking additional memory cells that are activated until thenumber of activated memory cells matches the total number. When thenumber of activated memory cells of the user data matches the totalnumber, the auto-referenced read techniques may stop applying the readvoltage to the memory array and determine that all the activated memorycells of the user data has the first logic state (e.g., SET or RESETcells). Additionally, the auto-referenced read techniques may determinethat remaining memory cells of the user data (e.g., the inactive memorycells when the number of activated memory cells matches thepredetermined number) have a second logic state (e.g., SET or RESETcells).

In some cases, the counting information is encoded to have a fixednumber of bits of a first logic state (e.g., a logic state of 1) priorto being stored in the additional set of memory cells. As an example,one-half of the additional set of memory cells may be configured to havethe logic state of 1 to represent the count information. During a readoperation, the auto-referenced read may track a number of activatedmemory cells of the additional set of memory cells to determine if allthe memory cells of the additional set of memory cells having the logicstate of 1 are accounted for. When all the memory cells of theadditional set of memory cells has been accounted for (e.g., activated),the auto-referenced read techniques may set a flag in a memory deviceand extract the counting information from the additional set of memorycells. The counting information may be stored in a register in thememory device and the flag may indicate that the counting information inthe register is a valid representation (e.g., in binary format) of atotal number of bits in the user data exhibiting a first logic state(e.g., a logic state of 1). The counting information in the register maythen be used to track a number of memory cells activated in the userdata in a similar manner described above. In some embodiments, adifferent read voltage may be applied to the additional set of memorycells compared to the memory cells storing the user data. Additionallyor alternatively, a single read voltage may be applied to both theadditional set of memory cells and the memory cells storing the userdata.

Features of the disclosure introduced above are further described belowin the context of a memory array in a memory device. Specificnon-limiting examples are then described for illustrating variousfeatures of the auto-referenced memory cell read techniques inaccordance with some embodiments (e.g., the memory array including PCMcells or 3DXP memory cells). These and other features of the disclosureare further illustrated by and described with reference to apparatusdiagrams, system diagrams, and flowcharts that relate to auto-referencedmemory cell read techniques. As a person of ordinary skill in the artwould appreciate, however, other alternatives and different variationsmay be considered and fall within the scope of this disclosure.

FIG. 1 illustrates an example memory device 100 in accordance withembodiments of the present disclosure. Memory device 100 may also bereferred to as an electronic memory apparatus. FIG. 1 is an illustrativerepresentation of various components and features of the memory device100. As such, it should be appreciated that the components and featuresof the memory device 100 shown to illustrate functionalinterrelationships, and may not be representative of their actualphysical positions within the memory device 100. In the illustrativeexample of FIG. 1, the memory device 100 includes a 3D memory array 102.The 3D memory array 102 includes memory cells 105 that may beprogrammable to store different states. In some embodiments, each memorycell 105 may be programmable to store two states, denoted as a logic 0and a logic 1. In some embodiments, a memory cell 105 may be configuredto store more than two logic states. A memory cell 105 may, in someembodiments, include a PCM cell (e.g., a 3DXP memory cell). Althoughsome elements included in FIG. 1 are labeled with a numeric indicator,other corresponding elements are not labeled, though they are the sameor would be understood to be similar, in an effort to increasevisibility and clarity of the depicted features.

The 3D memory array 102 may include two or more two-dimensional (2D)memory arrays formed adjacent one another (e.g., on top of or next toone another). This may increase a number of memory cells 105 that may beplaced or created on a single die or substrate as compared with 2Darrays, which in turn may reduce production costs, or increase theperformance of the memory device, or both. Based on the example depictedin FIG. 1, the 3D memory array 102 includes two levels of memory cells105; however, the number of levels may not be limited to two. Each levelmay be aligned or positioned such that memory cells 105 may be aligned(exactly, overlapping, or approximately) with one another across eachlevel, forming a memory cell stack 145. In some cases, the memory cellstack 145 may include a PCM cell (e.g., 3DXP memory cell) laid on top ofanother.

In some embodiments, each row of memory cells 105 is connected to anaccess line 110, and each column of memory cells 105 is connected to abit line 115. Access lines 110 and bit lines 115 may be substantiallyperpendicular to one another and may create an array of memory cells. Asshown in FIG. 1, the two memory cells 105 in a memory cell stack 145 mayshare a common conductive line such as a bit line 115. That is, a bitline 115 may be in electronic communication with the bottom electrode ofthe upper memory cell 105 and the top electrode of the lower memory cell105. In other embodiments, each of the memory cell 105 (e.g., the uppermemory cell, the lower memory cell) may be configured with its own bitline. In such cases, the memory cells may be separated by an insulationlayer. Other configurations may be possible, for example, a third layermay share an access line 110 with a lower layer. In general, one memorycell 105 may be located at the intersection of two conductive lines suchas an access line 110 and a bit line 115. This intersection may bereferred to as a memory cell's address. A target memory cell 105 may bea memory cell 105 located at the intersection of an energized accessline 110 and bit line 115; that is, access line 110 and bit line 115 maybe energized in order to read or write a memory cell 105 at theirintersection. Other memory cells 105 that are in electroniccommunication with (e.g., connected to) the same access line 110 or bitline 115 may be referred to as untargeted memory cells 105.

As discussed above, electrodes may be coupled to a memory cell 105 andan access line 110 or a bit line 115. The term electrode may refer to anelectrical conductor, and in some cases, may be employed as anelectrical contact to a memory cell 105. An electrode may include atrace, wire, conductive line, conductive layer, or the like thatprovides a conductive path between elements or components of memorydevice 100. In some embodiments, a memory cell 105 may include achalcogenide alloy positioned between a first electrode and a secondelectrode. One side of the first electrode may be coupled to an accessline 110 and the other side of the first electrode to the chalcogenidealloy. In addition, one side of the second electrode may be coupled to abit line 115 and the other side of the second electrode to thechalcogenide alloy. The first electrode and the second electrode may bethe same material (e.g., carbon) or different. In other embodiments, thememory cell 105 may include an additional electrode to separate thechalcogenide alloy into two parts as depicted in FIG. 2. A first part ofthe chalcogenide alloy may have a different composition than a secondpart of the chalcogenide alloy. In some embodiments, the first part ofthe chalcogenide alloy may have a different function than the secondpart of the chalcogenide alloy. The additional electrode may be the samematerial (e.g., carbon) or different than the first electrode and/or thesecond electrode.

Operations such as reading and writing may be performed on memory cells105 by energizing or selecting access line 110 and digit line 115. Insome embodiments, access lines 110 may also be known as word lines 110,and bit lines 115 may also be known as digit lines 115. References toword lines and bit lines, or their analogues, are interchangeablewithout loss of understanding or operation. Energizing or selecting aword line 110 or a digit line 115 may include applying a voltage to therespective line. Word lines 110 and digit lines 115 may be made ofconductive materials such as metals (e.g., copper (Cu), aluminum (Al),gold (Au), tungsten (W), titanium (Ti)), metal alloys, carbon,conductively-doped semiconductors, or other conductive materials,alloys, compounds, or the like.

In some architectures, the logic storing device of a memory cell 105(e.g., a capacitor, a resistor) may be electrically isolated from thedigit line 115 by a selection component. The word line 110 may beconnected to and may control the selection component. For example, theselection component may be a transistor and the word line 110 may beconnected to the gate of the transistor. Energizing the word line 110results in an electrical connection or closed circuit between the logicstoring device of a memory cell 105 and its corresponding digit line115. The digit line 115 may then be accessed to either read or write thememory cell 105. Upon selecting a memory cell 105, the resulting signalmay be used to determine the stored logic state. In some cases, a firstlogic state may correspond to no current or a negligibly small current,whereas a second logic state may correspond to a finite amount ofcurrent. In some cases, a memory cell 105 may include a 3DXP memory cellor a self-selecting memory cell, both having two terminals and may notneed a separate selection component. As such, one terminal of the 3DXPmemory cell or the self-selecting memory cell may be electricallyconnected to a word line 110 and the other terminal of the 3DXP memorycell or the self-selecting memory cell may be electrically connected toa digit line 115.

Accessing memory cells 105 may be controlled through a row decoder 120and a column decoder 130. For example, a row decoder 120 may receive arow address from the memory controller 140 and energize the appropriateword line 110 based on the received row address. Similarly, a columndecoder 130 may receive a column address from the memory controller 140and energize the appropriate digit line 115. For example, the 3D memoryarray 102 may include multiple word lines 110, labeled WL_B1 (or WL_T1)through WL_BM (or WL_TM), and multiple digit lines 115, labeled DL_1through DL_N, where M and N depend on the array size. Thus, byenergizing a word line 110 and a digit line 115, e.g., WL_B2 and DL_3,the memory cell 105 at their intersection may be accessed.

Upon accessing, a memory cell 105 may be read, or sensed, by sensecomponent 125 to determine the stored state of the memory cell 105. Forexample, a voltage may be applied to a memory cell 105 (using thecorresponding word line 110 and bit line 115) and the presence of aresulting current may depend on the applied voltage and the thresholdvoltage of the memory cell 105. In some cases, more than one voltage maybe applied. Additionally, if an applied voltage does not result incurrent flow, other voltages may be applied until a current is detectedby sense component 125. By assessing the voltage that resulted incurrent flow, the stored logic state of the memory cell 105 may bedetermined. In some cases, the voltage may be ramped up in magnitudeuntil a current flow is detected (e.g., a memory cell 105 turns on,switches on, conducts current, or becomes activated). In other cases,predetermined voltages may be applied sequentially until a current isdetected. Likewise, a current may be applied to a memory cell 105 andthe magnitude of the voltage to create the current may depend on theelectrical resistance or the threshold voltage of the memory cell 105.

Sense component 125 may include various transistors or amplifiers inorder to detect and amplify a difference in the signals, which may bereferred to as latching. The detected logic state of memory cell 105 maythen be output through column decoder 130 as output 135. In some cases,sense component 125 may be part of a column decoder 130 or row decoder120. Or, sense component 125 may be connected to or in electroniccommunication with column decoder 130 or row decoder 120. FIG. 1 alsoshows an alternative option of arranging the sense component 125-a (in adashed box). An ordinary person skilled in the art would appreciate thatsense component may be associated either with column decoder or rowdecoder without losing its functional purposes.

A memory cell 105 may be set or written by similarly energizing therelevant word line 110 and digit line 115 and at least one logic valuemay be stored in the memory cell 105. Column decoder 130 or row decoder120 may accept data, for example input/output 135, to be written to oneor more memory cells 105.

In some memory architectures, accessing the memory cell 105 may degradeor destroy the stored logic state and re-write or refresh operations maybe performed to return the original logic state to memory cell 105. InDRAM, for example, the capacitor may be partially or completelydischarged during a sense operation, corrupting the stored logic state.So the logic state may be re-written after a sense operation.Additionally, energizing a single word line 110 may result in thedischarge of all memory cells 105 in the row; thus, several or allmemory cells 105 in the row may need to be re-written. But innon-volatile memory, such as self-selecting memory, PCM (e.g., 3DXPmemory), FeRAM, or 3D NAND memory, accessing the memory cell 105 may notdestroy the logic state and, thus, the memory cell 105 may not requirere-writing after accessing.

The memory controller 140 may control the operation (e.g., read, write,re-write, refresh, discharge) of memory cells 105 through the variouscomponents, for example, row decoder 120, column decoder 130, and sensecomponent 125. In some cases, one or more of the row decoder 120, columndecoder 130, and sense component 125 may be co-located with the memorycontroller 140. Memory controller 140 may generate row and columnaddress signals in order to energize the desired word line 110 and digitline 115. Memory controller 140 may also generate and control variousvoltages or currents used during the operation of memory device 100.

The memory controller 140 may receive user data through the input/output135. In some embodiments, the memory controller 140 encodes the userdata to satisfy a condition prior to storing the user data in memorycells 105. The condition may be satisfied when encoded user data have apredetermined number of bits exhibiting a given logic state (e.g., alogic state of 1). As a way of example, the encoded user data may beconfigured to have 50% of the memory cells storing the encoded user datato exhibit the logic state of 1 while the other 50% of the memory cellsto exhibit a logic state of 0. This may be referred to as a balancedencoding process where half of the encoded user data bits have a logicstate of 1, and the other half have a logic state of 0. In someexamples, count data may be defined as the number of bits of the encodeduser data having given logic state (e.g., a logic state of 1 or a logicstate of 0), and the value of the count data may be encoded and storedby the memory controller 140 (e.g., in a register). During the encodingprocess, the memory controller 140 may add a certain number of bits(e.g., parity bits) to the user data to establish the predeterminednumber of memory cells to exhibit the given logic state. As a result ofadding the parity bits, the encoded user data may have more bits thanthe user data. In some embodiments, a different percentage value (e.g.,40%, 60%, 75%) of the memory cells exhibiting the logic state of 1 maybe employed during the encoding process, and as above, the encoded countdata representative of the number of bits of the encoded user datahaving a given logic state (e.g., a logic state of 1 or a logic state of0) may be stored by the memory controller 140 (e.g., in a register).Further, constant weight codes may be utilized in which all of thecodewords (e.g., the encoded user data with optional parity bits) mayhave the same number of bits of a given logic state regardless of thelength of the codeword. In such instances, the total percentage of bitshaving the given logic state may vary depending on the length of thecodeword, however the number of bits of encoded user data having thegiven logic state is the same across all codewords employing theconstant weight code scheme.

The memory controller 140 may apply a read voltage to the memory array102 to activate a group of memory cells 105 containing the encoded userdata with the predetermined number of bits exhibiting the given logicstate. The read voltage may have a constant rate of increase ormonotonically increasing staircase shape. The applied read voltage mayactivate a subset of the memory cells 105 containing the encoded userdata as a result of applying the read voltage when the applied readvoltage across the memory cells 105 exceeds their threshold voltages.The memory controller 140 may track the number of activated memory cells105 and compare the number to the predetermined number stored in theregister. When the number of activated memory cells 105 matches thepredetermined number, the memory controller 140 may determine that allthe memory cells exhibiting the given logic states are accounted for outof the group of memory cells containing the encoded user data and stopapplying to read voltage. Subsequently, the memory controller 140 maydetermine that all the activated memory cells 105 has the given logicstate.

In general, the amplitude, shape, polarity, and/or duration of anapplied voltage or current discussed herein may be adjusted or variedand may be different for the various operations discussed in operatingthe memory device 100. Furthermore, one, multiple, or all memory cells105 within memory array 102 may be accessed simultaneously; for example,multiple or all cells of memory array 102 may be accessed simultaneouslyduring a reset operation in which all memory cells 105, or a group ofmemory cells 105, are set to a single logic state.

FIG. 1 illustrates an example of a memory array 102 that supportsauto-referenced memory cell read techniques in accordance withembodiments of the present disclosure. Memory array 202 may be anexample of portions of memory array 102 described with reference toFIG. 1. As depicted in FIG. 2, memory array 202 includes multiplematerials to construct a memory cell 105-a. Each memory cell 105-a isstacked in a vertical direction (e.g., perpendicular to a substrate) tocreate memory cell stacks (e.g., the memory cell stack 145). The memorycell 105-a may be an example of a memory cell 105 described withreference to FIG. 1. Memory array 202 may thus be referred to as a 3Dmemory array. The architecture of memory array 202 may be referred to asa cross-point architecture. Although some elements included in FIG. 2are labeled with a numeric indicator, other corresponding elements arenot labeled, though they are the same or would be understood to besimilar, in an effort to increase visibility and clarity of the depictedfeatures.

Memory array 202 also includes word lines 110-a and bit lines 115-a,which may be examples of word line 110 and bit line 115 described withreference to FIG. 1. Illustration of the materials between the wordlines 110-a and the bit lines 115-a depicted in FIG. 2 may represent alower portion of the memory cell 105 in FIG. 1. Memory array 202includes electrodes 205, logic storage elements 210, selector deviceelements 220, and a substrate 225. In some examples, a single componentincluding a chalcogenide alloy (not shown, replacing selector deviceelement 220, logic storage element 210, and electrode 205-b) may act asboth a logic storage element and a selector device. Electrode 205-a maybe in electronic communication with bit line 115-a and electrode 205-cmay be in electronic communication with word line 110-a.

Insulating materials depicted as empty spaces may be both electricallyand thermally insulating. As described above, in PCM technology, variouslogic states may be stored by varying the electrical resistance of thelogic storage element 210 in memory cells 105-a, which in turnexhibiting varying threshold voltages of the memory cells 105-a. In somecases, storing various logic states includes passing a current throughthe memory cell 105-a, heating the logic storage element 210 in memorycell 105-a, or melting (e.g., wholly or partially) the material of thelogic storage element 210 in memory cell 105-a. Other storagemechanisms, such as threshold voltage modulation, may be exploited inchalcogenide-based memories.

In some cases, memory array 202 may include an array of memory cellstacks, and each memory cell stack may include multiple memory cells105-a. Memory array 202 may be made by forming a stack of conductivematerials, such as word lines 110-a, in which each conductive materialis separated from an adjacent conductive material by electricallyinsulating materials in between. The electrically insulating materialsmay include oxide or nitride materials, such as silicon oxide, siliconnitride, or other electrically insulating materials. These materials maybe formed above the substrate 225, such as a silicon wafer, or any othersemiconductor or oxide substrate. Subsequently, various process stepsmay be utilized to form the materials in between the word lines 110-aand bit lines 115-a such that each memory cell 105-a may be coupled witha word line 110-a and a bit line 115-a.

The selector device element 220 may be connected with the logic storageelement 210 through electrode 205-b. In some examples, the positioningof the selector device element 220 and the logic storage element 210 maybe flipped. The composite stack including the selector device element220, the electrode 205-b, and the logic storage element 210 may beconnected to a word line 110-a through the electrode 205-c and to a bitline 115-b through the electrode 205-a. The selector device element 220may aid in selecting a particular memory cell 105-a or may help preventstray currents from flowing through non-selected memory cells 105-aadjacent to a selected memory cell 105-a. The selector device element220 may include an electrically non-linear component (e.g., a non-Ohmiccomponent) such as a metal-insulator-metal (MIM) junction, an Ovonicthreshold switch (OTS), or a metal-semiconductor-metal (MSM) switch,among other types of two-terminal selector device such as a diode. Insome cases, the selector device element includes a chalcogenide alloy.The selector device, in some examples, include an alloy of selenium(Se), arsenic (As), silicon (Si), and germanium (Ge).

As discussed above, memory cells 105-a of FIG. 2 may include a materialwith a variable resistance. Variable resistance materials may refer tovarious material systems, including, for example, metal oxides,chalcogenides, and the like. Chalcogenide materials are materials oralloys that include at least one of the elements sulfur (S), tellurium(Te), or selenium (Se). Many chalcogenide alloys may be possible—forexample, a germanium-antimony-tellurium alloy (Ge—Sb—Te) is achalcogenide material. Other chalcogenide alloys not expressly recitedhere may also be employed.

To set a low-resistance state, a memory cell 105-a may be heated bypassing a current through the memory cell 105-a. Heating caused byelectrical current flowing through a material that has a finiteresistance may be referred to as Joule or Ohmic heating. Joule heatingmay thus be related to the electrical resistance of the electrodes orthe phase change material. Heating the phase change material to anelevated temperature (but below its melting temperature) may result inthe phase change material crystallizing and forming the low-resistancestate. In some cases, a memory cell 105-a may be heated by means otherthan Joule heating, for example, by using a laser. To set ahigh-resistance state, the phase change material may be heated above itsmelting temperature, for example, by Joule heating. The amorphousstructure of the molten material may be quenched, or locked in, byabruptly removing the applied current to quickly cool the phase changematerial.

In some cases, memory cells 105-a may exhibit different electricalcharacteristics after a number of cycling operations (e.g., a series ofread or write operations). For example, a threshold voltage of a memorycell 105-a (e.g., PCM cell) corresponding to a logic state of 1, afterreceiving an identical programming pulse to store the logic state of 1(e.g., a SET programming pulse), may be different if a memory cell 105-ais relatively new (e.g., a PCM cell with a small number of read or writeoperations) compared to a memory cell 105-a having been cycled throughan extensive number of read or write operations. In addition, in somecases, a chalcogenide material in the memory cells 105-a (e.g., thelogic storage element 210) may experience a change (which may also bereferred to as a drift) in its resistance after programming (e.g.,crystallizing or quenching) of the chalcogenide material during a writeoperation. Such change in resistance may result in changes in thresholdvoltages of memory cells 105-a and may hinder accurately readinginformation from memory cells 105-a (e.g., PCM cells) after a certainperiod of time elapsed. In some embodiments, the amount of change may bea function of an ambient temperature.

The auto-referenced read techniques may provide a robust read techniquewhen memory cells 105-a (e.g., PCM cells) exhibit different electricalcharacteristics described above. In some embodiments, the memory cells105-a may be configured to store encoded user data that include modifieduser data (or original user data, in some cases) and a number of paritybits, which may be added thereto. In some cases, the encoded user datastored in the memory cells 105-a have been modified to include apredetermined number of bits having the logic state of 1. The number ofbits having the logic state of 1 may be different depending on encodingscheme employed. In some cases, the number of bits having the logicstate of 1 may be 50% (or other percentage) of the bits containing theencoded user data. In some embodiments, the memory cells 105-a may beconfigured to store user data while an additional set of memory cells105-a is configured to store a counting information. The countinginformation may represent a number of bits in the user data having thelogic state of 1. In some cases, the counting information may be read inadvance to extract the number of bits in the user data having the logicstate of 1 before the user data are read. Additionally or alternatively,the counting information may be determined while the user data are beingread. The auto-referenced read techniques utilize encoding schemes thatprovide a precise number of memory cells 105-a having the logic state of1, which may in turn enable the auto-referenced read techniques to readuser data accurately regardless of the different electricalcharacteristics of memory cells described above.

FIG. 3A illustrate an example of user data pattern diagram 301 thatsupports auto-referenced memory cell read techniques in accordance withembodiments of the present disclosure. The user data pattern diagram 301includes user data 310-a and encoded user data 315-a. Encoding process320-a may convert the user data 310-a into the encoded user data 315-a.The encoded user data 315-a may be stored in a set of memory cells,which may be examples of memory cells 105 described with reference toFIGS. 1 and 2. Each box of the encoded user data 315-a may correspond toa memory cell (e.g., memory cell 105 or 105-a) that may exhibit a logicstate of 1 or a logic state of 0. During the encoding process 320-a, anumber of parity bits may be added to the user data 310-a to establish apredetermined number of bits of the encoded user data 315-a having agiven logic state (e.g., a logic state of 1). As a result, a number ofbits in the encoded user data 315-a may be greater than the number ofbits in the user data 310-a (e.g., n is larger than m if parity bits areadded). Decoding process 325 may convert the encoded user data 315-aback to the user data 310-a after the encoded user data 315-a has beenaccurately read.

In some embodiments, for each user data, corresponding encoded user datamay have a same number of memory cells exhibiting a logic state of 1 anda logic state of 0 (which may also be referred to as a balanced encodingscheme). As such, the encoded user data may be referred to have a 50%weight. In some embodiments, for each user data, corresponding encodeduser data may have a predetermined number of memory cells exhibiting agiven logic state (e.g., a logic state of 1), hence producing a constantweight that may be different than 50% (which may also be referred to asa constant weight encoding scheme). As described above, an outcome ofthe encoding process 320-a may be that a predetermined number of memorycells exhibiting a given logic state (e.g., a logic state of 1) in theencoded user data 315-a is established. The auto-referenced readtechniques may utilize the fact that such a predetermined number ofmemory cells exist for the encoding process 320-a (e.g., a balancedencoding scheme, a constant weight encoding scheme) to accurately readthe encoded user data 315-a as described below with reference to FIG.4A.

FIG. 3B illustrate an example of user data pattern diagram 302 thatsupports auto-referenced memory cell read techniques in accordance withembodiments of the present disclosure. The user data pattern diagram 302includes user data 310-b and encoded user data 315-b. Encoding process320-b may encode the user data 310-b into the encoded user data 315-b.The encoded user data may include the user data 310-b in addition tocount data 330. A number of memory cells of the count data 330 may bedetermined by a length of the user data 310-b. In some cases, the countdata 330 includes k memory cells when the user data is 2^(k) bits long.In other cases, the count data 330 may include 2×k memory cells when theuser data is 2^(k) bits long. The count data 330 may be stored in afirst set of memory cells (e.g., memory cell 105) that share a commonaccess line (e.g., word line 110) with a second set of memory cells(e.g., memory cell 105) that stores the user data 310-b. In some cases,the count data 330 are stored in a first set of memory cells (e.g.,memory cell 105) that does not share a common access line (e.g., wordline 110) with a second set of memory cells (e.g., memory cell 105) thatstores the user data 310-b.

In some embodiments, during the encoding process 320-b, a total numberbits having a given logic state (e.g., a logic state of 1) of the userdata 310-b may be identified and the total number may be stored in thecount data 330 (e.g., as a binary number). As an example, when the userdata 310-b is 16 bits long (e.g., 2⁴ bits long) and has 9 bits out of 16bits having a logic state of 1, the count data 330 is 4 bits long andcorresponds to a binary number 1001. In other embodiments, during theencoding process 320-b, the total number bits exhibiting a given logicstate (e.g., a logic state of 1) of the user data 310-b may beidentified and the total number may be encoded in the count data 330 byconverting each digit of the binary number (e.g., 1001) to a pair ofdigits (e.g., a binary digit of 1 to 10 and a binary digit of 0 to 01).Using the same example described above, when the user data 310-b is 16bits long (e.g., 2⁴ bits long) and has 9 bits (e.g., a binary number of1001) exhibiting a logic state of 1, the count data 330 may be 8 bitslong and correspond to 10010110. Such an encoding provides the countdata 330 to have a balanced weight of 50%. As described above, anoutcome of the encoding process 320-b may be that a known number ofmemory cells having a given logic state (e.g., a logic state of 1) inthe user data 310-b is established and stored in the count data 330. Theauto-referenced read techniques may utilize such a number available foreach user data 310-b to accurately read the user data 310-b as describedbelow with reference to FIG. 4B.

FIG. 4A illustrates an exemplary diagram 401 that supportauto-referenced memory cell read techniques in accordance with variousembodiments of the present disclosure. The diagram 401 illustrates aread voltage 405 (e.g., V_(READ)) applied to memory cells (e.g., memorycells 105 described with reference to FIGS. 1 and 2) that stores encodeduser data (e.g., encoded user data 315-a described with reference toFIG. 3A). The encoded user data may be configured to have apredetermined number of memory cells to exhibit a given logic state(e.g., a logic state of 1). The read voltage may be applied to thememory cells through a bit line (e.g., bit lines 115 described withreference to FIGS. 1 and 2) and a word line (e.g., word lines 110described with reference to FIGS. 1 and 2). In some embodiments, theread voltage 405 has a constant ramp rate as depicted in FIG. 4A. Insome embodiments, the read voltage 405 has a monotonically increasingstaircase shape. The diagram 401 illustrates that a subset of the memorycells activates in response to the read voltage 405. Each upward arrowin FIG. 4A represents one memory cell switching event (e.g., a memorycell 105 activates, turns on, switches on).

The diagram 401 also illustrates that the encoded user data (e.g.,encoded user data 315-a) is configured with a predetermined number, Nbits exhibiting a logic state of 1, for example. The auto-referencedread techniques may initialize a counter (which may also be referred toas a dynamic counter) in a memory device. The auto-referenced readtechniques may also store the predetermined number N in the memorydevice. At time T₀, the read voltage 405 may be applied to the memorycells storing the encoded user data. An initial value of the readvoltage 405 may be less than a lowest threshold voltage of the memorycells such that none of the memory cells activates at time T₀. In somecases, the initial value of the read voltage 405 may be greater than thelowest threshold voltage of the memory cells (not shown) such that anumber of memory cells activates at time T₀. At time T₁, a first memorycell may activate when the read voltage 405 applied to the first memorycell exceeds a threshold voltage associated with the first memory cell.The auto-referenced read techniques may update the counter to one torecord that the first memory cell has activated. Subsequently theauto-referenced read techniques may compare the number stored at thecounter to the predetermined number N. When the number in the counter isless than the predetermined number N, application of the read voltage405 to the memory cells continues. The auto-referenced read techniquesmay track additional number of memory cells activated (e.g., memorycells activated at T₂, T₃, and so on) as the read voltage 405 continuesto increase and update the counter.

At time T_(N), an Nth memory cell may activate as the read voltage 405applied to the Nth memory cell exceeds a threshold voltage associatedwith the Nth memory cell. The auto-referenced read techniques update thecounter to N based on the activation of the Nth memory cell and comparethe number stored in the counter with the predetermined number N. Theauto-referenced read techniques may determine that the number stored inthe counter matches with the predetermined number N and stop applyingthe read voltage 405. Subsequently, the auto-referenced read techniquesmay determine the activated memory cells (e.g., memory cellscorresponding to switching events at time T₁ through T_(N)) correspondto the logic state of 1. Additionally, the auto-referenced readtechniques may determine the remaining memory cells (e.g., memory cellsremaining unactivated until the Nth switching event) correspond to thelogic state of 0 (e.g., the memory cells associated with thresholdvoltages higher than the threshold voltages of the activated memorycells). After reading the encoded user data (e.g., encoded user data315-a) using the auto-referenced read techniques, the user data (e.g.,user data 310-a) may be decoded using a decoding process (e.g., decodingprocess 325). In other embodiments, after stopping applying the readvoltage 405, the user data (e.g., encoded user data 310-b described withreference to FIG. 3B) are output.

In some embodiments, the auto-referenced read techniques may utilize amean value estimating scheme based on properties of order statistics inwhich a single probability density function representing a particularweight of encoded user data may be used. By way of example, a singleprobability density function representing a weight of 50% (e.g., 64 bitsof a 128 bits encoded user data having a logic state of 1 under thebalanced coding scheme) may be used to determine that a jth switchingevent as an estimated median value of the threshold voltage distributionof the 64 bits having the logic state of 1. The determination of the jthswitching event may be associated with an uncertainty U_(j), which maybe heuristically expressed as U_(j)=2×3.54 σ₆₄ where σ₆₄ represents astandard deviation of the probability distribution function associatedwith the given j value for the known case of 64 bits having the logicstate of 1 (e.g., 50% weight under the balanced coding scheme) and ahalf-width of the threshold voltage distribution is estimated in termsof a standard deviation associated with a predetermined acceptable errorrate. Further, the auto-referenced read techniques may determine aduration to maintain the read voltage 405 after the jth switching eventto accurately detect additional memory cells exhibiting the logic stateof 1. In some cases, applying the read voltage 405 may continue for aduration of time after it is determined that the appropriate readingvoltage has been reached (e.g., to provide some margin).

FIG. 4B illustrates an exemplary diagram 402 that supportsauto-referenced memory cell read techniques in accordance with variousembodiments of the present disclosure. The diagram 402 illustrates userdata 410, first count data 420-a, and second count data 420-b. The userdata 410 may be an example of the user data 310 described with referenceto FIG. 3B. The first counting data 420-a and the second count data420-b may be examples of the count data 330 described with reference toFIG. 3B. The count data (e.g., 420-a or 420-b) may be stored in a firstset of memory cells (e.g., memory cell 105) that share a common accessline (e.g., word line 110) with a second set of memory cells (e.g.,memory cell 105) that stores the user data 410. In some cases, the countdata (e.g., 420-a or 420-b) are stored in a first set of memory cells(e.g., memory cell 105) that does not share a common access line (e.g.,word line 110) with a second set of memory cells (e.g., memory cell 105)that stores the user data 410. Additionally, the diagram 402 illustratesa first read voltage 405-a applied to the memory cells storing the countdata 420-b and a second read voltage 405-b applied to the memory cellsstoring the user data 410. The first read voltage 405-a and the secondread voltage 405-b may be examples of the read voltage 405 describedwith reference to FIG. 4A. The diagram 402 illustrates that a subset ofthe memory cells activates in response to the read voltage 405. Eachupward arrow in FIG. 4B represents one memory cell switching event(e.g., a memory cell 105 activates, turns on, switches on).

During an encoding stage, the auto-referenced read techniques may employan encoding process (e.g., encoding process 320-b described withreference to FIG. 3B) to identify a total number of bits having a givenlogic state (e.g., a logic state of 1) and store the total number inmemory cells corresponding to the count data 420. Combination of theuser data 410 and the count data 420 may represent encoded user data425. The user data 425 may be an example of the encoded user data 315-bdescribed with reference to FIG. 3B.

In some embodiments, the total number of bits of the user data 410having the logic state of 1 may be stored in the count data 420-a as abinary number. As a way of example, when the user data 410 is 16 bitslong (e.g., 2⁴ bits long) and has 9 bits out of 16 bits having a logicstate of 1, the count data 420-a is 4 bits long and corresponds to abinary number 1001. During a read operation, the auto-referenced readtechniques may read the total number from the count data 420-a (e.g.,1001 or 9) before applying the read voltage 405-a to the memory cellsstoring the user data 410. The auto-referenced read techniques may storethe total number in a set of DRAM cells or a register in a memory deviceand initialize a counter (which may be referred to as a dynamic counter)in the memory device. The auto-referenced read techniques may thenutilize similar steps described with reference to FIG. 4A.

At time the auto-referenced read may apply the read voltage 405-b to thememory cells storing the user data 410. The auto-referenced readtechniques may update the counter (e.g., the dynamic counter) as asubset of the memory cells storing the user data 410 activates. Theauto-referenced read techniques compare the number in the counter (e.g.,the dynamic counter) to the number stored in the DRAM cells or theregister (e.g., 9) and determine whether to continue application of theread voltage 405-b. At time T_(f), when 9th memory cell activates, theauto-referenced read techniques may update the number in the counter to9 and determine that the number in the counter matches the total numberstored in the DRAM cells or the register and stop applying the readvoltage 405-b. Subsequently, the auto-referenced read techniques maydetermine the activated memory cells (e.g., memory cells activated bythe time T_(f)) correspond to the logic state of 1 and that theremaining memory cells (e.g., memory cells remaining inactive by thetime T_(f)) correspond to the logic state of 0 (e.g., the memory cellsassociated with threshold voltages higher than the threshold voltages ofthe activated memory cells).

In some embodiments, the total number bits exhibiting a given logicstate (e.g., a logic state of 1) of the user data 410 may be identifiedand the total number may be encoded in the count data 420-b byconverting each digit of the binary number (e.g., 1001) to a pair ofdigits (e.g., a binary digit of 1 to 10 and a binary digit of 0 to 01).Each pair of digits 422 may represent the single binary digit of 1 or 0.By way of example, the pair of digits 422-a or 422-d may represent abinary digit of 1. The pair of digits 422-b or 422-c may represent abinary digit of 0. Using the same example described above, when the userdata 410 is 16 bits long (e.g., 2⁴ bits long) and has 9 bits (e.g., abinary number of 1001) exhibiting a logic state of 1, the count data420-b may be 8 bits long and correspond to 10010110. Such an encodingprovides the count data 420-b to have a balanced weight of 50%. In otherwords, when a length of user data 410 is determined, a length of countdata 420-b is determined and one-half of the length of the count data420-b corresponds to the number of bits of the count data 420-b havingthe logic state of 1.

In some embodiments, a number (e.g., a threshold) representing one-halfof the length of the count data 420-b may be stored in a memory device.The number (e.g., 4 in the example depicted in FIG. 4B) may correspondto the number of bits of the count data 420-b exhibiting a logic 1. Theauto-referenced read techniques may initiate a first counter to track anumber of memory cells activated out of the memory cells that stores theuser data 410 and a second counter to track a number of memory cellsactivated out of the memory cells that stores the count data 420-b. Theauto-referenced read may apply the read voltage 405-a to the memorycells storing the count data at time T₀. The auto-referenced readtechniques may update a number in the second counter to track a numberof memory cells activated in response to the read voltage 405-a. Theauto-referenced read techniques may compare the number in the secondcounter to the number (e.g., the threshold) stored in the memory deviceand determine whether the number in the second counter matches to thenumber (e.g., the threshold). The auto-referenced read techniques maycontinue applying the read voltage 405-a to the memory cells storing thecount data 420-b when the number in the second counter is less than thenumber (e.g., the threshold). At time T₁, the last memory cellexhibiting the logic state of 1 may activate out of the memory cellsstoring the count data 420-b. The last memory cell is a 4th memory cellin the example depicted in FIG. 4B. The auto-referenced read techniquesmay update the second counter and determine the number in the secondcounter (e.g., 4) matches with the number (e.g., the threshold).Subsequently, the auto-referenced read techniques may stop applying theread voltage 405-a to the memory cells storing the count data 420-b andread the information stored in the count data 420-b (e.g., reading 9 outof 10010110). In some embodiments, the auto-referenced read techniquesmay set a flag in a memory device as valid to indicate that the totalnumber of bits exhibiting a logic state of 1 in the user data 410 hasbeen identified.

In some embodiments, the auto-referenced read may apply the read voltage405-b to the memory cells storing the user data 410 at time T_(i). Theauto-referenced read techniques may update a number in the first counterto track a number of memory cells activated in response to the readvoltage 405-a. The auto-referenced read techniques may compare thenumber in the first counter to the number identified and indicated asvalid by the flag to determine whether the number in the first countermatches to the number identified and indicated as valid by the flag. Theauto-referenced read techniques may continue applying the read voltage405-b to the memory cells storing the user data 410 when the number inthe first counter is less than the number identified and indicated asvalid by the flag. At time T_(f), the last memory cell (e.g., the 9thmemory cell of FIG. 4B) exhibiting the logic state of 1 may activate outof the memory cells storing the user data 410. The auto-referenced readtechniques may update the first counter and determine the number in thefirst counter (e.g., 9) matches with the number identified and indicatedas valid. Subsequently, the auto-referenced read techniques may stopapplying the read voltage 405-b to the memory cells storing the userdata 410 and determine that the activated memory cells (e.g., memorycells corresponding to switching events during T_(i) through T_(f))correspond to the logic state of 1 and that the remaining memory cells(e.g., memory cells remaining inactive by the time T_(f)) correspond tothe logic state of 0 (e.g., the memory cells associated with thresholdvoltages higher than the threshold voltages of the activated memorycells).

In some embodiments, the read voltage 405-b applied to the memory cellsstoring the user data 410 may have an offset 430 in comparison to theread voltage 405-a applied to the memory cells storing the count data420-b. In some embodiments, the read voltage 405-a and the read voltage405-b may have a different slope (e.g., a ramp rate). In some instances,the read voltage 405-a may have a greater slope than the read voltage405-b. In some cases, a single read voltage may function as both theread voltage 405-a and the read voltage 405-b. In some aspects, thecount data 420-b may be stored in a first set of memory cells (e.g.,memory cell 105) that share a common access line (e.g., word line 110)with a second set of memory cells (e.g., memory cell 105) that storesthe user data 410 and a single read voltage may be applied to both thefirst set of memory cells and the second set of memory cells.

In some embodiments, each pair of digits 422 may be configured to couplewith a toggle indicator. In the example depicted in FIG. 4B, a total offour toggle indicators (not shown) may be coupled to the count data420-b, one toggle indicator for each pair of digits 422 (e.g., 422-a,422-b, 422-c, and 422-d). Each toggle indicator may be configured totrigger when one of two memory cells corresponding to the pair activatesin response to a read voltage (e.g., the read voltage 405-a). Outputs ofeach toggle indicator may be further configured to set a flag in amemory device when all the toggle indicators has been triggered (e.g.,all the pairs of digits 422 have one of two memory cells activated). Theauto-referenced read techniques may read the information stored in thecount data 420-b (e.g., reading 9 out of 10010110) based on the flagbeing set as valid. The flag also indicates that the total number ofbits exhibiting a logic state of 1 in the user data 410 has beenidentified. As described above, the auto-referenced read techniques mayutilize the total number of bits exhibiting a logic state of 1 in theuser data 410 to accurately determine application of the read voltage405-b to the memory cells storing the user data 410 and identify all thememory cells corresponding to the logic state of 1.

As described in FIGS. 4A and 4B, when both the count data 420 and theuser data 410 are simultaneously addressed by a same read voltage, usinga pair of digits 422-a, 422-b, 422-c, 422-d to represent each bit ofcount data 420-a (e.g., as depicted in count data 420-b) may allow forthe determination of the number of bits of the user data 410 having alogic state of 1 before any cell having a logic state of 0 thresholds inthe count data 420-a and/or 420-b and in the user data 410. In someexamples, at least one of the memory cells in each pair of bits 422 maythreshold before or at time T_(N) (or time T₁).

FIG. 5 shows a block diagram 500 of a memory array 505 that supportsauto-referenced memory cell read techniques in accordance withembodiments of the present disclosure. The memory array 505 may bereferred to as an electronic memory apparatus, and may be an example ofa component of a memory device 100 as described herein.

The memory array 505 may include one or more memory cells 510, a memorycontroller 515, a word line 520, a reference component 530, a sensecomponent 535, a digit line 540, and a latch 545. These components maybe in electronic communication with each other and may perform one ormore of the functions described herein. In some cases, the memory cells510 may include 3DXP memory cells. In some aspects, the memorycontroller 515 may include a biasing component 550 and a timingcomponent 555. In some embodiments, a sense component 535 may serve asthe reference component 530. In other cases, the reference component 530may be optional. Also, FIG. 7 shows an alternative schematic option ofarranging a sense component 536, a latch 545, and a reference component531 (in dashed boxes). An ordinary person skilled in the art wouldappreciate that the sense component and the associated components (i.e.,the latch 545 and the reference component 530) may be associated eitherwith a column decoder or a row decoder without losing their functionalpurposes.

The memory controller 515 may be in electronic communication with theword line 520, the digit line 540, and the sense component 535, whichmay be examples of the word line 110, the digit line 115, and the sensecomponent 125 described with reference to FIGS. 1 and 2. The componentsof the memory array 505 may be in electronic communication with eachother and may perform aspects of the functions described with referenceto FIGS. 1 through 4. In some cases, the reference component 530, thesense component 535, and the latch 545 may be components of the memorycontroller 515.

In some embodiments, the digit line 540 is in electronic communicationwith the sense component 535 and a memory cell 510. The memory cell 510may be writable with a logic state (e.g., a first, second, or thirdlogic state). The word line 520 may be in electronic communication withthe memory controller 515 and the memory cell 510. The sense component535 may be in electronic communication with the memory controller 515,the digit line 540, the latch 545, and the reference line 560. Thereference component 530 may be in electronic communication with thememory controller 515 and the reference line 560. A sense control line565 may be in electronic communication with the sense component 535 andthe memory controller 515. These components may also be in electroniccommunication with other components, both inside and outside of thememory array 505, in addition to components not listed above, via othercomponents, connections, or buses.

The memory controller 515 may be configured to energize the word line520 or the digit line 540 by applying voltages to those various nodes.For example, the biasing component 550 may be configured to apply avoltage to operate the memory cell 510 to read or write the memory cell510 as described above. In some cases, the memory controller 515 mayinclude a row decoder, a column decoder, or both, as described herein.This may enable the memory controller 515 to access one or more memorycells 105 as illustrated with reference to FIG. 1. The biasing component550 may also provide voltage to the reference component 530 in order togenerate a reference signal for the sense component 535. Additionally,the biasing component 550 may provide voltages for the operation of thesense component 535.

In some embodiments, the memory controller 515 may perform itsoperations using the timing component 555. For example, the timingcomponent 555 may control the timing of the various word line selectionsor bit line biasing, including timing for switching and voltageapplication to perform the memory functions, such as reading andwriting, discussed herein. In some cases, the timing component 555 maycontrol the operations of the biasing component 550.

The reference component 530 may include various components to generate areference signal for the sense component 535. The reference component530 may include circuitry configured to produce a reference signal. Insome cases, the reference component 530 may be implemented using other3DXP memory cells. The sense component 535 may compare a signal from thememory cell 510 (through the digit line 540) with a reference signalfrom the reference component 530. Upon determining the logic state, thesense component may then store the output in the latch 545, where it maybe used in accordance with the operations of an electronic device thatthe memory array 505 is a part. The sense component 535 may include asense amplifier in electronic communication with the latch 545 and thememory cell 510.

The memory controller 515 and/or at least some of its varioussub-components may be implemented in hardware, software executed by aprocessor, firmware, or any combination thereof. If implemented insoftware executed by a processor, the functions of the memory controller515 and/or at least some of its various sub-components may be executedby a general-purpose processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), an field-programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described in the presentdisclosure. The memory controller 515 and/or at least some of itsvarious sub-components may be physically located at various positions,including being distributed such that portions of functions areimplemented at different physical locations by one or more physicaldevices. In some embodiments, the memory controller 515 and/or at leastsome of its various sub-components may be a separate and distinctcomponent in accordance with various embodiments of the presentdisclosure. In other examples, the memory controller 515 and/or at leastsome of its various sub-components may be combined with one or moreother hardware components, including but not limited to an I/Ocomponent, a transceiver, a network server, another computing device,one or more other components described in the present disclosure, or acombination thereof in accordance with various embodiments of thepresent disclosure.

The memory controller 515 may apply a voltage (e.g., a read voltage) toa memory array configured to activate a group of memory cells containingencoded user data during a read operation. The voltage may increase as afunction of time with a constant rate of change. The memory controller515 may track a number of memory cells turning on (e.g., activating) inresponse to the read voltage. In some embodiments, the memory controller515 may compare the number of activated memory cells with apredetermined number stored in a memory device when the encoded userdata have been encoded with the predetermined number of memory cells tohave the first logic state. When the number of activated memory cellsmatches the predetermined number, the memory controller 515 may stopapplying the read voltage to the memory array and determine that all theactivated memory cells of the encoded user data has the first logicstate (e.g., SET or RESET cells). Additionally, the memory controller515 may determine that remaining memory cells of the encoded user data(e.g., the inactive memory cells when the number of activated memorycells matches the predetermined number) have the second logic state(e.g., SET or RESET cells).

FIG. 6 shows a block diagram 600 of a memory controller 615 thatsupports auto-referenced memory cell read techniques in accordance withembodiments of the present disclosure. The memory controller 615 may bean example of the memory controller 515 described with reference to FIG.5. The memory controller 615 may include biasing component 620, timingcomponent 625, counting component 630, detecting component 635,comparing component 640, read component 645, input/output component 650,programming component 655, encoding component 660, and flag component665. Each of these modules may communicate, directly or indirectly, withone another (e.g., via one or more buses).

The biasing component 620 may activate at least a portion of a firstgroup of memory cells of the memory array by applying a read voltage tothe memory array and activate a first subset of the first portion ofmemory cells by applying a first read voltage to the memory array and asecond subset of the second portion of memory cells by applying a secondread voltage to the memory array. The biasing component 620 may activatea first subset of the first portion of memory cells by applying a firstread voltage to the memory array, and activate at least one cell of eachpair of the set of pairs by applying a second read voltage to the memoryarray.

In some embodiments, the biasing component 620 may stop application ofthe second read voltage based on the determination that the second valuesatisfies the threshold, stop application of the read voltage to thememory array based on the determination that the first value satisfiesthe threshold, where the one or more memory cells are read afterapplication of the read voltage has stopped. The biasing component 620may maintain application of the first read voltage based on thedetermination that the first value does not correspond to the identifiedtotal number, maintain application of the second read voltage based onthe determination that the second value does not satisfy the threshold,and maintain application of the read voltage to the memory array basedon the determination that the first value does not satisfy thethreshold.

In some embodiments, the biasing component 620 may stop application ofthe first read voltage based on the determination that the first valuecorresponds to the identified total number, where the one or more memorycells of the first portion of memory cells are read after application ofthe first read voltage has stopped. In some cases, the first group ofmemory cells are configured with a predetermined number of memory cellshaving a first logic state. In some examples, the first group of memorycells are configured with a fixed number of memory cells independent ofa total number of memory cells in the first group. In some aspects, afirst half of the first group of memory cells corresponds to a firstlogic state and a second half of the first group of memory cellscorresponds to a second logic state.

In some embodiments, the read voltage includes a set of constantvoltages each having a different value over a duration. In some aspects,the first read voltage and the second read voltage are a same singleread voltage. In some instances, the first read voltage is configured tohave a time offset with respect to the second read voltage. In someexamples, the first read voltage is configured to have a different rateof voltage change with respect to the second read voltage.

The counting component 630 may initialize a counter in a controllercoupled with a memory array, update the counter to a first value basedon determining that the set of memory cells has been activated, andupdate the counter to a second value based on determining that thesecond set of memory cells has been activated, where the one or morememory cells are read based on updating the counter to the second value.In some embodiments, the counting component 630 may initialize a firstcounter and a second counter in a controller coupled with a memory arraythat includes a first portion of memory cells and a second portion ofmemory cells, and update the first counter to a first value based onactivating the first subset of memory cells and the second counter to asecond value based on activating the second subset of memory cells. Insome cases, the counting component 630 may initialize a counter in acontroller coupled with a memory array that includes a first portion ofmemory cells and a second portion of memory cells, where the secondportion of memory cells includes a set of pairs of memory cells, eachpair of the set of pairs associated with a respective flag value, andupdate the counter to a first count value based on activation of thefirst subset of memory cells.

Detecting component 635 may determine that a set of memory cells hasbeen activated based on applying the read voltage and determine that asecond set of memory cells has been activated based on maintainingapplication of the read voltage. In some instances, each memory cell ofthe set of memory cells corresponds to a first logic state. In somecases, the set of memory cells is half of the first group of memorycells.

Comparing component 640 may compare the first value of the updatedcounter to a threshold stored at the controller, compare the first countvalue to the determined total number, where one or more memory cells ofthe first portion of memory cells are read based on the comparison, andcompare the second value of the updated second counter to a thresholdstored at the controller, where reading one or more memory cells of thefirst portion of memory cells is based on comparing the second value ofthe updated second counter to the threshold. In some embodiments, thecomparing component 640 may identify, from the second portion of memorycells, a total number of memory cells of the first portion having afirst logic state based on the determination that the second valuesatisfies the threshold, determine that the first value corresponds tothe identified total number, and determine that the first value does notcorrespond to the identified total number.

In some cases, the comparing further includes: determining that thefirst value does not satisfy the threshold stored at the controller. Insome aspects, the threshold is equal to the predetermined number ofmemory cells having the first logic state. In some instances, thethreshold is read from a second group of memory cells of the memoryarray. In some cases, the comparing further includes: determining thatthe first value satisfies the threshold stored at the controller. Insome embodiments, the comparing further includes: determining that thesecond value does not satisfy the threshold stored at the controller. Insome examples, the comparing further includes: determining that thesecond value satisfies the threshold stored at the controller.

Read component 645 may read one or more memory cells of the memory arraybased on the comparison, determine that the set of memory cells that hasbeen activated corresponds to a first logic state, read one or morememory cells of the first portion of memory cells based on updating thefirst counter and the second counter, and read one or more memory cellsof the first portion of memory cells based on the indicator. In someembodiments, the read component 645 may determine, based on a set ofvalues of the second portion of memory cells after activation of the atleast one cell, a total number of memory cells of the first portionhaving a first logic state. In some cases, the first logic statecorresponds to a first set of threshold voltages which may be less thana second set of threshold voltages associated with a second logic state.

Input/output component 650 may receive, at a controller, a first set ofbits of an input vector from a host device.

Programming component 655 may allocate a block of memory to store thefirst set of bits of the input vector and a second set of bits based ona total number bits of the first set of bits and write the first set ofbits and the second set of bits at the block of memory. In some cases,the second set of bits includes multiple couples of bits representativeof the number of bits of the first set of bits having the first logicstate.

Encoding component 660 may generate the second set of bits based on anumber of bits of the first set of bits having a first logic state andgenerate a set of bit values corresponding to the determined number ofbits. In some cases, generating the second set of bits includes:determining the number of bits of the first set of bits having the firstlogic state.

Flag component 665 may set a flag in the controller based on identifyingthe total number of memory cells of the first portion having the firstlogic state and set an indicator in the controller based on activationof the at least one cell. In some cases, setting the indicator includes:toggling the respective flag value of each pair of the set of pairs froma first flag value to a second flag value based on activation of the atleast one cell.

FIG. 7 shows a diagram of a system 700 including a device 705 thatsupports auto-referenced memory cell read techniques in accordance withembodiments of the present disclosure. The device 705 may be an exampleof or include the components of memory device 100 as described above,e.g., with reference to FIG. 1. The device 705 may include componentsfor bi-directional voice and data communications including componentsfor transmitting and receiving communications, including a memorycontroller 715, memory cells 720, a basic input/output system (BIOS)component 725, a processor 730, an I/O controller 735, and peripheralcomponents 740. These components may be in electronic communication viaone or more buses (e.g., bus 710).

The memory controller 715 may operate one or more memory cells asdescribed herein. Specifically, the memory controller 715 may beconfigured to support auto-referenced memory cell read techniques. Insome cases, the memory controller 715 is coupled with the cross-pointarray and operable to perform access operations (e.g., programming orread) as described above with reference to FIG. 5. In some cases, thememory controller 715 may read a counting information from an additionalset of memory cells to determine a total number of bits in user datahaving a given logic state (e.g., a logic state of 1) when the user datahave been encoded with the additional set of memory cells that storesthe counting information corresponding to the total number. The memorycontroller 715 may use the total number to determine as to whether aread voltage applied to memory cells storing the user data may continueor stop while tracking a number of activated memory cells of the userdata in response to the read voltage. During a read operation, thememory controller 715 may also track a number of activated memory cellsof the additional set of memory cells to determine if all the memorycells of the additional set of memory cells having the logic state of 1has been accounted for. The memory controller 715 may set a flag in thememory device 705 and extract the counting information from theadditional set of memory cells. In some embodiments, the memorycontroller 715 stores the counting information in a register in thememory device 705 and the flag may indicate that the countinginformation in the register is valid.

The memory cells 720 may store information (i.e., in the form of alogical state) as described herein. In some embodiments, the memorycells 720 may include a cross-point memory array comprising 3DXP memorycells. The memory cells 720 may also be referred to as a memory medium.In some cases, the memory medium may include a 3D cross-point array ofphase change memory cells.

The BIOS component 725 be a software component that includes BIOSoperated as firmware, which may initialize and run various hardwarecomponents. The BIOS component 725 may also manage data flow between aprocessor and various other components, e.g., peripheral components 740,input/output control component, etc. The BIOS component 725 may includea program or software stored in read only memory (ROM), flash memory, orany other non-volatile memory.

The processor 730 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a central processing unit (CPU), amicrocontroller, an ASIC, an FPGA, a programmable logic device, adiscrete gate or transistor logic component, a discrete hardwarecomponent, or any combination thereof). In some cases, the processor 730may be configured to operate a memory array using a memory controller.In other cases, a memory controller may be integrated into the processor730. The processor 730 may be configured to execute computer-readableinstructions stored in a memory to perform various functions (e.g.,functions or tasks supporting auto-referenced memory cell readtechniques).

The I/O controller 735 may manage input and output signals for thedevice 705. The I/O controller 735 may also manage peripherals notintegrated into the device 705. In some cases, the I/O controller 735may represent a physical connection or port to an external peripheral.In some cases, the I/O controller 735 may utilize an operating systemsuch as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, oranother known operating system. In other cases, the I/O controller 735may represent or interact with a modem, a keyboard, a mouse, atouchscreen, or a similar device. In some cases, the I/O controller 735may be implemented as part of a processor. In some cases, a user mayinteract with the device 705 via the I/O controller 735 or via hardwarecomponents controlled by the I/O controller 735.

The peripheral components 740 may include any input or output device, oran interface for such devices. Examples may include disk controllers,sound controller, graphics controller, Ethernet controller, modem,universal serial bus (USB) controller, a serial or parallel port, orperipheral card slots, such as peripheral component interconnect (PCI)or accelerated graphics port (AGP) slots.

The input 745 may represent a device or signal external to the device705 that provides input to the device 705 or its components. This mayinclude a user interface or an interface with or between other devices.In some cases, the input 745 may be managed by the I/O controller 735,and may interact with the device 705 via the peripheral components 740.

The output 750 may also represent a device or signal external to thedevice 705 configured to receive output from the device 705 or any ofits components. Examples of the output 750 may include a display, audiospeakers, a printing device, another processor or printed circuit board,etc. In some cases, the output 750 may be a peripheral element thatinterfaces with the device 705 via the peripheral components 740. Insome cases, the output 750 may be managed by the I/O controller 735.

The components of the device 705 may include circuitry designed to carryout their functions. This may include various circuit elements, forexample, conductive lines, transistors, capacitors, inductors,resistors, amplifiers, or other active or inactive elements, configuredto carry out the functions described herein. The device 705 may be acomputer, a server, a laptop computer, a notebook computer, a tabletcomputer, a mobile phone, a wearable electronic device, a personalelectronic device, or the like. Or the device 705 may be a portion oraspect of such a device.

FIG. 8 shows a flowchart illustrating a method 800 for auto-referencedmemory cell read techniques with embodiments of the present disclosure.The operations of method 800 may be implemented by a memory device 100or its components as described herein. For example, the operations ofmethod 800 may be performed by a memory controller as described withreference to FIGS. 1 and 5 through 7. In some embodiments, the memorydevice 100 may execute a set of codes to control the functional elementsof the device to perform the functions described below. Additionally oralternatively, the memory device 100 may perform aspects of thefunctions described below using special-purpose hardware.

At 805 the memory device 100 may initialize a counter in a controllercoupled with a memory array. The operations of 805 may be performedaccording to the methods described herein. In certain examples, aspectsof the operations of 805 may be performed by a counting component asdescribed with reference to FIGS. 5 through 7.

At 810 the memory device 100 may activate at least a portion of a firstgroup of memory cells of the memory array by applying a read voltage tothe memory array. The operations of 810 may be performed according tothe methods described herein. In certain examples, aspects of theoperations of 810 may be performed by a biasing component as describedwith reference to FIGS. 5 through 7.

In some examples, the first group of memory cells are configured with afixed number of memory cells independent of a total number of memorycells in the first group. In some aspects, a first half of the firstgroup of memory cells corresponds to a first logic state and a secondhalf of the first group of memory cells corresponds to a second logicstate.

At 815 the memory device 100 may determine that a set of memory cellshas been activated based at least in part on applying the read voltage.The operations of 815 may be performed according to the methodsdescribed herein. In certain examples, aspects of the operations of 815may be performed by a detecting component as described with reference toFIGS. 5 through 7.

In some instances, each memory cell of the set of memory cellscorresponds to a first logic state. In some cases, the set of memorycells is half of the first group of memory cells.

At 820 the memory device 100 may update the counter to a first valuebased at least in part on determining that the set of memory cells hasbeen activated. The operations of 820 may be performed according to themethods described herein. In certain examples, aspects of the operationsof 820 may be performed by a counting component as described withreference to FIGS. 5 through 7.

At 825 the memory device 100 may compare the first value of the updatedcounter to a threshold stored at the controller. The operations of 825may be performed according to the methods described herein. In certainexamples, aspects of the operations of 825 may be performed by acomparing component as described with reference to FIGS. 5 through 7.

At 830 the memory device 100 may read one or more memory cells of thememory array based at least in part on the comparison. The operations of830 may be performed according to the methods described herein. Incertain examples, aspects of the operations of 830 may be performed by aread component as described with reference to FIGS. 5 through 7.

After one or more memory cells of the memory array are read at 830, thememory device 100 may decode these memory cells to obtain the decodeduser data bits.

An apparatus for performing the method 800 is described. The apparatusmay include means for initializing a counter in a controller coupledwith a memory array, means for activating at least a portion of a firstgroup of memory cells of the memory array by applying a read voltage tothe memory array, means for determining that a set of memory cells hasbeen activated based at least in part on applying the read voltage,means for updating the counter to a first value based at least in parton determining that the set of memory cells has been activated, meansfor comparing the first value of the updated counter to a thresholdstored at the controller, and means for reading one or more memory cellsof the memory array based at least in part on the comparison.

Another apparatus for operating a memory array is described. Anotherapparatus for performing the method 800 is described. The apparatus mayinclude a memory cell and a memory controller in electroniccommunication with the memory cell, wherein the memory controller isoperable to initialize a counter in a controller coupled with a memoryarray, activate at least a portion of a first group of memory cells ofthe memory array by applying a read voltage to the memory array,determine that a set of memory cells has been activated based at leastin part on applying the read voltage, update the counter to a firstvalue based at least in part on determining that the set of memory cellshas been activated, compare the first value of the updated counter to athreshold stored at the controller, and read one or more memory cells ofthe memory array based at least in part on the comparison.

In some examples of the method 800 and apparatus described above, thecomparing further comprises: determining that the first value satisfiesthe threshold stored at the controller. Some examples of the method 800and apparatus described above may further include processes, features,means, or instructions for stopping application of the read voltage tothe memory array based at least in part on the determination that thefirst value satisfies the threshold, wherein the one or more memorycells may be read after application of the read voltage may havestopped.

In some examples of the method 800 and apparatus described above, thecomparing further comprises: determining that the first value does notsatisfy the threshold stored at the controller. Some examples of themethod 800 and apparatus described above may further include processes,features, means, or instructions for maintaining application of the readvoltage to the memory array based at least in part on the determinationthat the first value does not satisfy the threshold. Some examples ofthe method 800 and apparatus described above may further includeprocesses, features, means, or instructions for determining that asecond set of memory cells may have been activated based at least inpart on maintaining application of the read voltage. Some examples ofthe method 800 and apparatus described above may further includeprocesses, features, means, or instructions for updating the counter toa second value based at least in part on determining that the second setof memory cells may have been activated, wherein the one or more memorycells may be read based at least in part on updating the counter to thesecond value.

Some examples of the method 800 and apparatus described above mayfurther include processes, features, means, or instructions fordetermining that the set of memory cells that may have been activatedcorresponds to a first logic state. In some examples of the method 800and apparatus described above, the first logic state corresponds to afirst set of threshold voltages that may be less than a second set ofthreshold voltages associated with a second logic state. In someexamples of the method 800 and apparatus described above, the firstgroup of memory cells may be configured with a predetermined number ofmemory cells having a first logic state. In some examples of the method800 and apparatus described above, the threshold may be equal to thepredetermined number of memory cells having the first logic state. Insome examples of the method 800 and apparatus described above, thethreshold may be read from a second group of memory cells of the memoryarray. In some examples of the method 800 and apparatus described above,the read voltage comprises a plurality of constant voltages each havinga different value over a duration.

FIG. 9 shows a flowchart illustrating a method 900 for auto-referencedmemory cell read techniques with embodiments of the present disclosure.The operations of method 900 may be implemented by a memory device 100or its components as described herein. For example, the operations ofmethod 900 may be performed by a memory controller as described withreference to FIGS. 1 and 5 through 7. In some embodiments, the memorydevice 100 may execute a set of codes to control the functional elementsof the device to perform the functions described below. Additionally oralternatively, the memory device 100 may perform aspects of thefunctions described below using special-purpose hardware.

At 905 the memory device 100 may receive, at a controller, a first setof bits of an input vector from a host device. The operations of 905 maybe performed according to the methods described herein. In certainexamples, aspects of the operations of 905 may be performed byinput/output component as described with reference to FIGS. 5 through 7.

At 910 the memory device 100 may allocate a block of memory to store thefirst set of bits of the input vector and a second set of bits based atleast in part on a total number bits of the first set of bits. Theoperations of 910 may be performed according to the methods describedherein. In certain examples, aspects of the operations of 910 may beperformed by a programming component as described with reference toFIGS. 5 through 7.

At 915 the memory device 100 may generate the second set of bits basedat least in part on a number of bits of the first set of bits having afirst logic state. The operations of 915 may be performed according tothe methods described herein. In certain examples, aspects of theoperations of 915 may be performed by encoding component as describedwith reference to FIGS. 5 through 7.

At 920 the memory device 100 may write the first set of bits and thesecond set of bits at the block of memory. The operations of 920 may beperformed according to the methods described herein. In certainexamples, aspects of the operations of 920 may be performed by aprogramming component as described with reference to FIGS. 5 through 7.

An apparatus for performing the method 900 is described. The apparatusmay include means for receiving, at a controller, a first set of bits ofan input vector from a host device, means for allocating a block ofmemory to store the first set of bits of the input vector and a secondset of bits based at least in part on a total number bits of the firstset of bits, means for generating the second set of bits based at leastin part on a number of bits of the first set of bits having a firstlogic state, and means for writing the first set of bits and the secondset of bits at the block of memory.

Another apparatus for performing the method 900 is described. Theapparatus may include a memory cell and a memory controller inelectronic communication with the memory cell, wherein the memorycontroller is operable to receive, at a controller, a first set of bitsof an input vector from a host device, allocate a block of memory tostore the first set of bits of the input vector and a second set of bitsbased at least in part on a total number bits of the first set of bits,generate the second set of bits based at least in part on a number ofbits of the first set of bits having a first logic state, and write thefirst set of bits and the second set of bits at the block of memory.

In some examples of the method 900 and apparatus described above, thesecond set of bits comprises multiple couples of bits representative ofthe number of bits of the first set of bits having the first logicstate. In some examples of the method 900 and apparatus described above,generating the second set of bits comprises: determining the number ofbits of the first set of bits having the first logic state. Someexamples of the method 900 and apparatus described above may furtherinclude processes, features, means, or instructions for generating a setof bit values corresponding to the determined number of bits.

FIG. 10 shows a flowchart illustrating a method 1000 for auto-referencedmemory cell read techniques with embodiments of the present disclosure.The operations of method 1000 may be implemented by a memory device 100or its components as described herein. For example, the operations ofmethod 1000 may be performed by a memory controller as described withreference to FIGS. 1 and 5 through 7. In some embodiments, the memorydevice 100 may execute a set of codes to control the functional elementsof the device to perform the functions described below. Additionally oralternatively, the memory device 100 may perform aspects of thefunctions described below using special-purpose hardware.

At 1005 the memory device 100 may initialize a first counter and asecond counter in a controller coupled with a memory array thatcomprises a first portion of memory cells and a second portion of memorycells. The operations of 1005 may be performed according to the methodsdescribed herein. In certain examples, aspects of the operations of 1005may be performed by a counting component as described with reference toFIGS. 5 through 7.

At 1010 the memory device 100 may activate a first subset of the firstportion of memory cells by applying a first read voltage to the memoryarray and a second subset of the second portion of memory cells byapplying a second read voltage to the memory array. The operations of1010 may be performed according to the methods described herein. Incertain examples, aspects of the operations of 1010 may be performed bya biasing component as described with reference to FIGS. 5 through 7.

At 1015 the memory device 100 may update the first counter to a firstvalue based at least in part on activating the first subset of memorycells and the second counter to a second value based at least in part onactivating the second subset of memory cells. The operations of 1015 maybe performed according to the methods described herein. In certainexamples, aspects of the operations of 1015 may be performed by acounting component as described with reference to FIGS. 5 through 7.

At 1020 the memory device 100 may read one or more memory cells of thefirst portion of memory cells based at least in part on updating thefirst counter and the second counter. The operations of 1020 may beperformed according to the methods described herein. In certainexamples, aspects of the operations of 1020 may be performed by a readcomponent as described with reference to FIGS. 5 through 7.

An apparatus for performing the method 1000 is described. The apparatusmay include means for initializing a first counter and a second counterin a controller coupled with a memory array that comprises a firstportion of memory cells and a second portion of memory cells, means foractivating a first subset of the first portion of memory cells byapplying a first read voltage to the memory array and a second subset ofthe second portion of memory cells by applying a second read voltage tothe memory array, means for updating the first counter to a first valuebased at least in part on activating the first subset of memory cellsand the second counter to a second value based at least in part onactivating the second subset of memory cells, and means for reading oneor more memory cells of the first portion of memory cells based at leastin part on updating the first counter and the second counter.

Another apparatus for performing the method 1000 is described. Theapparatus may include a memory cell and a memory controller inelectronic communication with the memory cell, wherein the memorycontroller is operable to initialize a first counter and a secondcounter in a controller coupled with a memory array that comprises afirst portion of memory cells and a second portion of memory cells,activate a first subset of the first portion of memory cells by applyinga first read voltage to the memory array and a second subset of thesecond portion of memory cells by applying a second read voltage to thememory array, update the first counter to a first value based at leastin part on activating the first subset of memory cells and the secondcounter to a second value based at least in part on activating thesecond subset of memory cells, and read one or more memory cells of thefirst portion of memory cells based at least in part on updating thefirst counter and the second counter.

Some examples of the method 1000 and apparatus described above mayfurther include processes, features, means, or instructions forcomparing the second value of the updated second counter to a thresholdstored at the controller, wherein reading one or more memory cells ofthe first portion of memory cells may be based at least in part oncomparing the second value of the updated second counter to thethreshold.

In some examples of the method 1000 and apparatus described above, thecomparing further comprises: determining that the second value satisfiesthe threshold stored at the controller. Some examples of the method 1000and apparatus described above may further include processes, features,means, or instructions for stopping application of the second readvoltage based at least in part on the determination that the secondvalue satisfies the threshold. Some examples of the method 1000 andapparatus described above may further include processes, features,means, or instructions for identifying, from the second portion ofmemory cells, a total number of memory cells of the first portion havinga first logic state based at least in part on the determination that thesecond value satisfies the threshold.

Some examples of the method 1000 and apparatus described above mayfurther include processes, features, means, or instructions fordetermining that the first value corresponds to the identified totalnumber. Some examples of the method 1000 and apparatus described abovemay further include processes, features, means, or instructions forstopping application of the first read voltage based at least in part onthe determination that the first value corresponds to the identifiedtotal number, wherein the one or more memory cells of the first portionof memory cells may be read after application of the first read voltagemay have stopped.

Some examples of the method 1000 and apparatus described above mayfurther include processes, features, means, or instructions fordetermining that the first value does not correspond to the identifiedtotal number. Some examples of the method 1000 and apparatus describedabove may further include processes, features, means, or instructionsfor maintaining application of the first read voltage based at least inpart on the determination that the first value does not correspond tothe identified total number. Some examples of the method 1000 andapparatus described above may further include processes, features,means, or instructions for setting a flag in the controller based atleast in part on identifying the total number of memory cells of thefirst portion having the first logic state.

In some examples of the method 1000 and apparatus described above, thecomparing further comprises: determining that the second value does notsatisfy the threshold stored at the controller. Some examples of themethod 1000 and apparatus described above may further include processes,features, means, or instructions for maintaining application of thesecond read voltage based at least in part on the determination that thesecond value does not satisfy the threshold. In some examples of themethod 1000 and apparatus described above, the first read voltage andthe second read voltage may be a same single read voltage. In someexamples of the method 1000 and apparatus described above, the firstread voltage may be configured to may have a time offset with respect tothe second read voltage. In some examples of the method 1000 andapparatus described above, the first read voltage may be configured tomay have a different rate of voltage change with respect to the secondread voltage.

FIG. 11 shows a flowchart illustrating a method 1100 for auto-referencedmemory cell read techniques with embodiments of the present disclosure.The operations of method 1100 may be implemented by a memory device 100or its components as described herein. For example, the operations ofmethod 1100 may be performed by a memory controller as described withreference to FIGS. 1 and 5 through 7. In some embodiments, the memorydevice 100 may execute a set of codes to control the functional elementsof the device to perform the functions described below. Additionally oralternatively, the memory device 100 may perform aspects of thefunctions described below using special-purpose hardware.

At 1105 the memory device 100 may initialize a counter in a controllercoupled with a memory array that comprises a first portion of memorycells and a second portion of memory cells, wherein the second portionof memory cells comprises a plurality of pairs of memory cells, eachpair of the plurality of pairs associated with a respective flag value.The operations of 1105 may be performed according to the methodsdescribed herein. In certain examples, aspects of the operations of 1105may be performed by a counting component as described with reference toFIGS. 5 through 7.

At 1110 the memory device 100 may activate a first subset of the firstportion of memory cells by applying a first read voltage to the memoryarray. The operations of 1110 may be performed according to the methodsdescribed herein. In certain examples, aspects of the operations of 1110may be performed by a biasing component as described with reference toFIGS. 5 through 7.

At 1115 the memory device 100 may activate at least one cell of eachpair of the plurality of pairs by applying a second read voltage to thememory array. The operations of 1115 may be performed according to themethods described herein. In certain examples, aspects of the operationsof 1115 may be performed by a biasing component as described withreference to FIGS. 5 through 7.

At 1120 the memory device 100 may set an indicator in the controllerbased at least in part on activation of the at least one cell. Theoperations of 1120 may be performed according to the methods describedherein. In certain examples, aspects of the operations of 1120 may beperformed by a flag component as described with reference to FIGS. 5through 7.

At 1125 the memory device 100 may read one or more memory cells of thefirst portion of memory cells based at least in part on the indicator.The operations of 1125 may be performed according to the methodsdescribed herein. In certain examples, aspects of the operations of 1125may be performed by a read component as described with reference toFIGS. 5 through 7.

An apparatus for performing the method 1100 is described. The apparatusmay include means for initializing a counter in a controller coupledwith a memory array that comprises a first portion of memory cells and asecond portion of memory cells, wherein the second portion of memorycells comprises a plurality of pairs of memory cells, each pair of theplurality of pairs associated with a respective flag value, means foractivating a first subset of the first portion of memory cells byapplying a first read voltage to the memory array, means for activatingat least one cell of each pair of the plurality of pairs by applying asecond read voltage to the memory array, means for setting an indicatorin the controller based at least in part on activation of the at leastone cell, and means for reading one or more memory cells of the firstportion of memory cells based at least in part on the indicator.

Another apparatus for performing the method 1100 is described. Theapparatus may include a memory cell and a memory controller inelectronic communication with the memory cell, wherein the memorycontroller is operable to initialize a counter in a controller coupledwith a memory array that comprises a first portion of memory cells and asecond portion of memory cells, wherein the second portion of memorycells comprises a plurality of pairs of memory cells, each pair of theplurality of pairs associated with a respective flag value, activate afirst subset of the first portion of memory cells by applying a firstread voltage to the memory array, activate at least one cell of eachpair of the plurality of pairs by applying a second read voltage to thememory array, set an indicator in the controller based at least in parton activation of the at least one cell, and read one or more memorycells of the first portion of memory cells based at least in part on theindicator.

In some examples of the method 1100 and apparatus described above,setting the indicator comprises: toggling the respective flag value ofeach pair of the plurality of pairs from a first flag value to a secondflag value based at least in part on activation of the at least onecell.

Some examples of the method 1100 and apparatus described above mayfurther include processes, features, means, or instructions fordetermining, based at least in part on a set of values of the secondportion of memory cells after activation of the at least one cell, atotal number of memory cells of the first portion having a first logicstate. Some examples of the method 1100 and apparatus described abovemay further include processes, features, means, or instructions forupdating the counter to a first count value based at least in part onactivation of the first subset of memory cells. Some examples of themethod 1100 and apparatus described above may further include processes,features, means, or instructions for comparing the first count value tothe determined total number, wherein one or more memory cells of thefirst portion of memory cells may be read based at least in part on thecomparison.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Furthermore, embodiments from two or more of the methods may becombined.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof. Some drawings may illustrate signals as a single signal;however, it will be understood by a person of ordinary skill in the artthat the signal may represent a bus of signals, where the bus may have avariety of bit widths.

The term “electronic communication” and “coupled” refer to arelationship between components that support electron flow between thecomponents. This may include a direct connection between components ormay include intermediate components. Components in electroniccommunication or coupled to one another may be actively exchangingelectrons or signals (e.g., in an energized circuit) or may not beactively exchanging electrons or signals (e.g., in a de-energizedcircuit) but may be configured and operable to exchange electrons orsignals upon a circuit being energized. By way of example, twocomponents physically connected via a switch (e.g., a transistor) are inelectronic communication or may be coupled regardless of the state ofthe switch (i.e., open or closed).

As used herein, the term “substantially” means that the modifiedcharacteristic (e.g., a verb or adjective modified by the termsubstantially) need not be absolute but is close enough so as to achievethe advantages of the characteristic.

As used herein, the term “electrode” may refer to an electricalconductor, and in some cases, may be employed as an electrical contactto a memory cell or other component of a memory array. An electrode mayinclude a trace, wire, conductive line, conductive layer, or the likethat provides a conductive path between elements or components of memorydevice 100.

Chalcogenide materials may be materials or alloys that include at leastone of the elements S, Se, and Te. Phase change materials discussedherein may be chalcogenide materials. Chalcogenide materials may includealloys of S, Se, Te, Ge, As, Al, Sb, Au, indium (In), gallium (Ga), tin(Sn), bismuth (Bi), palladium (Pd), cobalt (Co), oxygen (O), silver(Ag), nickel (Ni), platinum (Pt). Example chalcogenide materials andalloys may include, but are not limited to, Ge—Te, In—Se, Sb—Te, Ga—Sb,In—Sb, As—Te, Al—Te, Ge—Sb—Te, Te—Ge—As, In—Sb—Te, Te—Sn—Se, Ge—Se—Ga,Bi—Se—Sb, Ga—Se—Te, Sn—Sb—Te, In—Sb—Ge, Te—Ge—Sb—S, Te—Ge—Sn—O,Te—Ge—Sn—Au, Pd—Te—Ge—Sn, In—Se—Ti—Co, Ge—Sb—Te—Pd, Ge—Sb—Te—Co,Sb—Te—Bi—Se, Ag—In—Sb—Te, Ge—Sb—Se—Te, Ge—Sn—Sb—Te, Ge—Te—Sn—Ni,Ge—Te—Sn—Pd, or Ge—Te—Sn—Pt. The hyphenated chemical compositionnotation, as used herein, indicates the elements included in aparticular compound or alloy and is intended to represent allstoichiometries involving the indicated elements. For example, Ge—Te mayinclude Ge_(x)Te_(y), where x and y may be any positive integer. Otherexamples of variable resistance materials may include binary metal oxidematerials or mixed valence oxide including two or more metals, e.g.,transition metals, alkaline earth metals, and/or rare earth metals.Embodiments are not limited to a particular variable resistance materialor materials associated with the memory elements of the memory cells.For example, other examples of variable resistance materials can be usedto form memory elements and may include chalcogenide materials, colossalmagnetoresistive materials, or polymer-based materials, among others.

The term “isolated” refers to a relationship between components in whichelectrons are not presently capable of flowing between them; componentsare isolated from each other if there is an open circuit between them.For example, two components physically connected by a switch may beisolated from each other when the switch is open.

The devices discussed herein, including a memory device 100, may beformed on a semiconductor substrate, such as silicon, germanium,silicon-germanium alloy, gallium arsenide, gallium nitride, etc. In somecases, the substrate is a semiconductor wafer. In other cases, thesubstrate may be a silicon-on-insulator (SOI) substrate, such assilicon-on-glass (SOG) or silicon-on-sapphire (SOP), or epitaxial layersof semiconductor materials on another substrate. The conductivity of thesubstrate, or sub-regions of the substrate, may be controlled throughdoping using various chemical species including, but not limited to,phosphorous, boron, or arsenic. Doping may be performed during theinitial formation or growth of the substrate, by ion-implantation, or byany other doping means.

A transistor or transistors discussed herein may represent afield-effect transistor (FET) and comprise a three terminal deviceincluding a source, drain, and gate. The terminals may be connected toother electronic elements through conductive materials, e.g., metals.The source and drain may be conductive and may comprise a heavily-doped,e.g., degenerate, semiconductor region. The source and drain may beseparated by a lightly-doped semiconductor region or channel. If thechannel is n-type (i.e., majority carriers are electrons), then the FETmay be referred to as a n-type FET. If the channel is p-type (i.e.,majority carriers are holes), then the FET may be referred to as ap-type FET. The channel may be capped by an insulating gate oxide. Thechannel conductivity may be controlled by applying a voltage to thegate. For example, applying a positive voltage or negative voltage to ann-type FET or a p-type FET, respectively, may result in the channelbecoming conductive. A transistor may be “on” or “activated” when avoltage greater than or equal to the transistor's threshold voltage isapplied to the transistor gate. The transistor may be “off” or“deactivated” when a voltage less than the transistor's thresholdvoltage is applied to the transistor gate.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a DSP, an ASIC, an FPGA or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general-purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a digital signal processor (DSP) and a microprocessor, multiplemicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of at least one of A, B, or C meansA or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, asused herein, the phrase “based on” shall not be construed as a referenceto a closed set of conditions. For example, an exemplary step that isdescribed as “based on condition A” may be based on both a condition Aand a condition B without departing from the scope of the presentdisclosure. In other words, as used herein, the phrase “based on” shallbe construed in the same manner as the phrase “based at least in parton.”

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, DSL, orwireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include CD, laser disc, optical disc, digital versatile disc (DVD),floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

1. (canceled)
 2. A method, comprising: initializing a first counter anda second counter in a controller coupled with a memory array thatcomprises a first portion of memory cells and a second portion of memorycells; activating a first subset of the first portion of memory cells byapplying a first read voltage to the memory array and a second subset ofthe second portion of memory cells by applying a second read voltage tothe memory array; updating the first counter to a first value based atleast in part on activating the first subset of the first portion ofmemory cells and the second counter to a second value based at least inpart on activating the second subset of the second portion of memorycells; and reading one or more memory cells of the first portion ofmemory cells based at least in part on updating the first counter andthe second counter.
 3. The method of claim 2, further comprising:comparing the second value of the updated second counter to a threshold,wherein reading one or more memory cells of the first portion of memorycells is based at least in part on comparing the second value of theupdated second counter to the threshold.
 4. The method of claim 3,wherein the comparing further comprises: determining that the secondvalue satisfies the threshold; stopping application of the second readvoltage based at least in part on the determination that the secondvalue satisfies the threshold; and identifying, from the second portionof memory cells, a total number of memory cells of the first portionhaving a first logic state based at least in part on the determinationthat the second value satisfies the threshold.
 5. The method of claim 4,further comprising: determining that the first value corresponds to theidentified total number; and stopping application of the first readvoltage based at least in part on the determination that the first valuecorresponds to the identified total number, wherein the one or morememory cells of the first portion of memory cells are read afterapplication of the first read voltage has stopped.
 6. The method ofclaim 4, further comprising: determining that the first value does notcorrespond to the identified total number; and maintaining applicationof the first read voltage based at least in part on the determinationthat the first value does not correspond to the identified total number.7. The method of claim 4, further comprising: setting a flag in thecontroller based at least in part on identifying the total number ofmemory cells of the first portion having the first logic state.
 8. Themethod of claim 3, wherein the comparing further comprises: determiningthat the second value does not satisfy the threshold; and maintainingapplication of the second read voltage based at least in part on thedetermination that the second value does not satisfy the threshold. 9.The method of claim 2, wherein the first read voltage and the secondread voltage are a same single read voltage.
 10. The method of claim 2,wherein the first read voltage is configured to have a time offset withrespect to the second read voltage.
 11. The method of claim 2, whereinthe first read voltage is configured to have a different rate of voltagechange with respect to the second read voltage.
 12. An apparatus,comprising: a memory array that comprises a first portion of memorycells and a second portion of memory cells; and a controller coupledwith the memory array and operable to cause the apparatus to: initializea first counter and a second counter; activate a first subset of thefirst portion of memory cells by applying a first read voltage to thememory array and a second subset of the second portion of memory cellsby applying a second read voltage to the memory array; update the firstcounter to a first value based at least in part on activating the firstsubset of the first portion of memory cells and the second counter to asecond value based at least in part on activating the second subset ofthe second portion of memory cells; and read one or more memory cells ofthe first portion of memory cells based at least in part on updating thefirst counter and the second counter.
 13. The apparatus of claim 12,wherein the controller is further operable to cause the apparatus to:compare the second value of the updated second counter to a threshold,wherein reading one or more memory cells of the first portion of memorycells is based at least in part on comparing the second value of theupdated second counter to the threshold.
 14. The apparatus of claim 13,wherein the controller is further operable to cause the apparatus to:determine that the second value satisfies the threshold; stopapplication of the second read voltage based at least in part on thedetermination that the second value satisfies the threshold; andidentify, from the second portion of memory cells, a total number ofmemory cells of the first portion having a first logic state based atleast in part on the determination that the second value satisfies thethreshold, wherein the comparing is based at least in part on theidentifying.
 15. The apparatus of claim 14, wherein the controller isfurther operable to cause the apparatus to: determine that the firstvalue corresponds to the identified total number; and stop applicationof the first read voltage based at least in part on the determinationthat the first value corresponds to the identified total number, whereinthe one or more memory cells of the first portion of memory cells areread after application of the first read voltage has stopped.
 16. Theapparatus of claim 14, wherein the controller is further operable tocause the apparatus to: determine that the first value does notcorrespond to the identified total number; and maintain application ofthe first read voltage based at least in part on the determination thatthe first value does not correspond to the identified total number. 17.The apparatus of claim 14, wherein the controller is further operable tocause the apparatus to: set a flag in the controller based at least inpart on identifying the total number of memory cells of the firstportion having the first logic state.
 18. The apparatus of claim 12,wherein the first read voltage is configured to have a time offset withrespect to the second read voltage.
 19. An apparatus, comprising: amemory array that comprises a first portion of memory cells and a secondportion of memory cells; a biasing component coupled with the memoryarray and operable to activate a first subset of the first portion ofmemory cells by applying a first read voltage to the memory array and asecond subset of the second portion of memory cells by applying a secondread voltage to the memory array; a controller coupled with the memoryarray and operable to cause the apparatus to: initialize a first counterand a second counter in the controller; and update the first counter toa first value based at least in part on the biasing component activatingthe first subset of the first portion of memory cells and the secondcounter to a second value based at least in part on activating thesecond subset of the second portion of memory cells; and a sensecomponent operable to read one or more memory cells of the first portionof memory cells based at least in part on the first counter and thesecond counter being updated.
 20. The apparatus of claim 19, wherein thecontroller is further operable to: compare the second value of theupdated second counter to a threshold, wherein reading one or morememory cells of the first portion of memory cells is based at least inpart on comparing the second value of the updated second counter to thethreshold.
 21. The apparatus of claim 20, wherein: the controller isfurther operable to determine that the second value satisfies thethreshold; the biasing component is further operable to stop applicationof the second read voltage based at least in part on the determinationthat the second value satisfies the threshold; and the controller isfurther operable to identify, from the second portion of memory cells, atotal number of memory cells of the first portion having a first logicstate based at least in part on the determination that the second valuesatisfies the threshold.